In geothermal power plants, hot fluid from a geothermal resource is extracted via a production well from the interior of the earth to the ground surface. The extracted hot fluid is used for power production either directly when converted to steam and expanded in a turbine, or indirectly by means of a binary cycle power plant whereby the extracted hot fluid is brought in heat exchanger relation with the motive fluid of the power plant, such as organic motive fluid. The heat depleted geothermal liquid is returned to the interior of the earth via an injection well, which is separated from the production well to avoid mixing of the hot fluid that is extracted in the production well. The injected geothermal liquid becomes reheated and is returned to the production well via a rock fracture.
As a result of continuous exploitation of the geothermal resource, the enthalpy of the extracted fluid, and/or pressure tends to decrease over the course of time, reducing the economic viability of a power plant for producing power from the extracted geothermal resource. Such production wells consequently cease to be exploited for power production, and are hereafter referred to as “sub-commercial” wells. These sub-commercial wells render much financial damage to developers of the geothermal power plant after investing a significant amount of capital in drilling and maintaining the well.
Attempts have been made to improve the productivity of a sub-commercial well by a stimulation method.
U.S. 2012/0181034 discloses a method for stimulating an underground reservoir formation by introducing a particulate diverting agent into a well, to thereby temporarily seal passages within a fracture near the wellbore face and to isolate the fracture from the well. When a stimulation fluid is applied to the well at a sufficient pressure, an additional fracture is produced by hydroshearing such that it is expanded under shear. Rather than causing permanent damage to the permeability of the fractures which will lead to a reduction in economic value of the geothermal resource, the particulate diverting agent is able to degrade over an extended time.
One disadvantage of this stimulation method relates to its unpredictability since it is unknown where the induced fracture will be produced and whether the induced fracture will lead to stimulation of the sub-commercial well.
It is therefore an object of the present invention to provide a method for selecting a location of a stimulating well from where there exists a high probability that an induced fracture will lead to stimulation of a sub-commercial well.
Other objects and advantages of the invention will become apparent as the description proceeds.